1. Field of the Invention
This invention relates to a developer for developing electrostatic latent images, which is used for electrophotography.
2. Description of the Prior Art
In recent years, much higher image quality is required in the fields of electrophotographic copying machines and printers. To satisfy this requirement, various efforts have been made to the toner particle size small.
However, making the toner particle size small causes the specific surface area of the toner to increase, resulting in poor fluidity of the toner. From the viewpoint of improvement of fluidity, it is effective to spheroidize the toner to minimize the specific surface area of the toner.
The spherical toner is, in general, manufactured by a wet granulation method. Almost all the toner particles obtained by this method are spherical. Consequently, in the blade cleaning process, toner particles are likely to pass through the blade, frequently causing cleaning failure.
On the other hand, cleaning failure can be prevented by making the toner shape nonspherical with respect to the toner form. Nonspherical toners are, in general, manufactured by a kneading-pulverizing method. The toners manufactured in this way are almost all nonspherical and have large specific surface area, causing poor fluidity. The fluidity of nonspherical toners can be improved, for example, by increasing the addition of fluidizing agents such as silica, but in such a case, problems of degraded environmental-resistance, generation of low-charged toners and fogging associated with it, and the similar problems occur.
The effects of the toner shape on toner properties as described above are more serious in a one-component developing method. In the one-component developing method, the toner is fed to surface of a toner supporting member and is rubbed and charged electrically while a toner thin layer is being formed on the supporting member by a regulating member of toner layer thickness. The electrostatic latent image is developed by the thin layer of the toner on the supporting member.
The one-component developing method as described above depends on a form of the regulating member of toner layer thickness and a regulated pressure. That is, if the toner primarily consists of spherical particles, the toner fluidity increases but on the contrary, it becomes difficult to regulate the toner in the thin layer state by the regulating member because toner particles pass through the regulating member. To prevent this problem, it is necessary to increase the regulating pressure, but this will cause sticking and fusion of the toner components on the regulating member and sleeve surface.
On the other hand, for the nonspherical toner, toner fluidity is degraded. Therefore, increasing regulation of the toner prevents the toner from being transported on the sleeve through the clearance between the sleeve and the regulating member. This needs to relaxing the regulating pressure, but this will lose a chance for the toner to come in sufficient contact with the sleeve and/or the regulating member, and the toner is unable to be thoroughly charged. As a result, image noises such as fogging and the like as well as machine contamination occur due to generation of low-charged toners and reversely charged toners by frictional electrification between toners.